Introduction and Structure of Bacteria PDF

Introduction and Structure of bacteria Asst. prof. Dr. Wasan Abdul-elah Bakir  Objective 1. Define of medical microbiology 2. Classification of Microorganisms 3. Microbes that Cause Infectious Diseases 4. Important Features of Microbes 5...

Introduction and Structure of bacteria Asst. prof. Dr. Wasan Abdul-elah Bakir  Objective 1. Define of medical microbiology 2. Classification of Microorganisms 3. Microbes that Cause Infectious Diseases 4. Important Features of Microbes 5. Eukaryotes & Prokaryotes 6. Shape & Size of Bacteria 7. Structure of Bacteria a. Cell wall b. Cytoplasmic membrane c. Cytoplasm d. Structures outside the cell wall e. Bacterial spore Questions 2  Microbiology Medical microbiology is the study of the causative agents of infectious diseases of humans and the reaction to such infections. In other words it deals with pathogenesis, laboratory diagnosis, specific treatment and control of infection (immunization). Medical microbiology includes: Bacteriology – The science that study bacteria, the causative agents of a number of infectious diseases. Loading… Virology – The science that study viruses, non- cellular living systems, capable of causing infectious diseases in human being. Immunology – The science which concerned with mechanisms of body protection against pathogenic microorganisms and foreign cells and substances. Mycology – The science that deals with the study of fungi. ↑ Parasitology – study of protozoa and parasitic worms.  Microbiology Classification of Microorganisms:- Classification by structure Subcellular – DNA or RNA surrounded by a protein coat – viruses Prokaryotic – simple cell structure with no nucleus or organelles – bacteria Eukaryotic – complex cell structure with nucleus and specialized organelles – protozoa, fungi and worms.  Bacteriology What are bacteria? Bacteria are prokaryote cells (unicellular organisms) that reproduce by & - binary fission whereas eukaryotes divide by mitosis. T They have: 1- No nucleus 2-No organelles (endoplasmic reticulum, mitochondria, Golgi apparatus, lysosomes). Loading… They possess a cell wall which characteristically contains peptidoglycan. They have different ribosomes from eukaryotic cells with a sedimentation value 70S. Bacteria vary in size from 0.3 µm, to 5 µm, it is visible with the light microscope. The smallest bacteria (Mycoplasma) are about the same size as the largest viruses (poxviruses)  Bacteriology location i Bacteria can be found in every where on the earth. - They can live in variety of environment including ~ a wide range of temperature, PH, and salt concentration. Most bacteria are capable of independent survival and growth, but species Chlamydia and Rickettsia can only survive as intracellular organisms. They can be beneficial or harmful by causing diseases. & C & The bacteria in our bodies help degrade the food we eat, help make & nutrients available to us and neutralize toxins. & Also, they play an essential role in the defense against infections by protecting colonized surfaces from invading pathogens  Bacteriology SHAPE AND SIZE OF BACTERIA Bacteria are classified by shape into three basic groups: 00 cocci, bacilli, and spirochetes. The cocci are round, the bacilli are rods, and the spirochetes are spiral-shaped. Some bacteria, called vibrio, are shaped like slightly curved rods or comma-shaped Some bacteria are variable in shape and are said to be pleomorphic (many-shaped). The shape of a bacterium is determined by its rigid cell wall.  Bacteriology SHAPE AND SIZE OF BACTERIA The arrangement of bacteria is important. For example, certain cocci occur in pairs (diplococci), some in chains (streptococci), and others in grapelike clusters (staphylococci). among Cocci : ¨ Pairs………Diplococci ¨ Chains……streptococci ¨ Clusters…..Staphylococci ¨ In four……Tetrad  Structure of Bacteria *Essential components such as: Cell wall Cytoplasmic membrane Ribosome Nucleoid *Accessory components (not every bacteria has): Capsule havisecurePilus or fimbria, Flagella Spores, Plasmid, Transposons  Cell wall Cell wall: is a layer located outside the cell membrane which is rigid, porous and relatively permeable. Cell wall is the common component to all bacteria (except Mycoplasma species and Halobacterium halobium, which are bounded by a cell membrane, not a cell wall). Importance of cell wall: Loading… 1. Bacterial rigidity and shape 2. protection against osmotic changes 3. Porous to allow nutrients passage. 4. Take part in cell division 5. Has a target sites of antibiotics, lysozyme -- and bacteriophges. - o Structure differs in Gramlayer It has peptidoglycan positive made& of negative bacteria. long polysaccharide chains cross-linked by peptide bridges. o it provides rigidity and protection.  Cell wall The peptidoglycan layer in the bacterial cell wall: is a structure formed from linear chains of two alternating amino sugars, namely N- acetylglucosamine and N- acetylmuramic acid. The alternating sugars are connected by β- (1,4)- glycosidic bond. (this bond is the target of lysozyme). Loss of cell wall leads to death (this can be affected by some antibiotics and by lysozyme). Note: Lysozyme is a natural body defense substance that cleaves the link between N- acetylglucosamine and N-acetylmuramic acid, which leads to cell death. Found in 12 - bodily secretions such as tears, saliva, and milk. skin-respiritory + carical tract  Cell wall Most bacteria are classified as gram positive or gram negative cording to their response to the Gram-staining procedure. In 1884, a bacteriologist named Christian Gram created a test (Gram's stain ) that could determine if a bacterium had a thick, mesh-like membrane called peptidoglycan. Bacteria with thick peptidoglycan are called gram positive. If the peptidoglycan layer is thin, it's classified as gram negative. Gram's stain differentiates all bacteria into two distinct groups: a. Gram-positive organisms b. Gram-negative organisms gram-positive bacteria purple in Colour while gram negative are red  Cell wall Why gram-positive bacteria purple in Colour while gram negative are red? During the procedure, crystal violet dye is applied to a sample of bacteria. Gram-positive bacteria have a thick layer of peptidoglycan in their cell walls (50–90% of cell wall), which retains the crystal violet and as a result are stained purple, whereas gram-negative bacteria have a thinner layer (10% of cell wall), so do not retain the purple stain and are counter-stained pink or red by safranin.  Cell wall *What is the difference between Gram positive and Gram negative cell wall? The gram-positive bacterial cell wall: thick layer of peptidoglycan, plasma membrane. The gram-negative bacterial cell wall: Outer membrane “ made of lipopolysaccharide and protein”, thin layer of peptidoglycan, plasma membrane. and have a periplasmic space where β-lactamases are found. Beta-lactamases are enzymes (EC 3.5.2.6) produced by bacteria that provide multi-resistance to beta-lactam antibiotics such as penicillins, cephalosporins,. The gram-positive cell wall: has a large amount of “teichoic acid” that binds to peptidoglycan and “lipoteichoic acid” that binds to plasma membrane. 15  Cell wall The outer membrane which is unique to gram negative bacteria. - The outer membrane (which protects the bacteria) differs from the cytoplasmic membrane in that it contains a special different lipid called lipopolysaccharide (LPS). o LPS is also known as endotoxin which is only found in gram negative - bacteria. It is responsible for many of the features of disease, such as fever and shock (especially hypotension), caused by these organisms. LPS is called endotoxin because it is an integral part of the cell wall, in contrast to exotoxins  Structure of Bacteria Cytoplasmic membrane: This elementary membrane, also known as the plasma membrane, semipermeable membrane. It is basically a double - layer of phospholipids with numerous proteins integrated into its structure. - Components of plasma membrane: lipid bilayer, integral and peripheral proteins, carbohydrates and cholesterol. Functions: 1. active transport of molecules into the cell 2. synthesis of precursors of the cell wall 3. Energy generation. 4. Secretion of toxins and enzymes 17  Structure of Bacteria Teichoic Acids: & & They are composed either glycerol phosphate or ribitol phosphate. bearing a strong negative charge (Give negative charge to outer surface of Gram positive). located in the outer layer of the gram-positive cell wall. They are strongly antigenic, but are generally absent in Gram-negative bacteria. Some of glycerol teichoic acid penetrate the peptidoglycan layer and are covalently linked to the lipid in the cytoplasmic membrane, in which case they are called lipoteichoic acid that are considered as bridges connecting cell membrane to cell wall in Gram positive bacteria. They are antigenic other molecule that and cytotoxic. toxin or indue immune response toxic to cen living  Structure of Bacteria Teichoic Acids: The medical importance of teichoic acid lies in their ability to: 1. Induce inflammation and septic shock when caused by certain Gram positive bacteria. 2. Teichoic acid also mediate the attachment of staphylococci to mucosal cell. COMPARISON OF CELL WALLS OF GRAM-POSITIVE AND GRAM-NEGATIVE BACTERIA  Structure of Bacteria Periplasmic space: Between the inner cell membrane and the outer membrane of gram- negative bacteria lies the periplasmic space, which is the location of β- lactamases—the enzymes that degrade β-lactam antibiotics, such as penicillins and cephalosporins.  Structure of Bacteria Cytoplasm: Is an aqueous environment. The cytoplasm has two distinct areas when seen in the electron microscope: 1. An amorphous matrix that contains ribosomes, nutrient granules, metabolites, and plasmids. 2. An inner, nucleoid region composed of DNA.  Structure of Bacteria RIBOSOMES Bacterial ribosomes are the site of protein synthesis as in eukaryotic cells. Bacterial ribosomes are 70S in size, with 50S and 30S subunits, whereas eukaryotic ribosomes are 80S in size, with 60S and 40S subunits. The ribosomes are the target of some antibiotics.  THE NUCLEOID Area of cytoplasm where bacterial DNA is located. DNA features are: The prokaryote Nucleoid ( the equivalent of the eukaryotic Nucleus) consists of a very thin, long, circular DNA molecular double strand that is not surrounded by a membrane and localized in the cytoplasm. PLASMIDS Some (not all) bacteria also have (an extra circular chromosomal DNA) called PLASMIDS, they are important at the gene transfer.  These are extra chromosomal circular DNA that are capable of replicating independent of the bacterial chromosome. 00 The plasmids mainly carry genes responsible for characteristics like fertility, antibiotic B resistance and production of bacteriocin (a protein that kills closely related bacteria). + & Plasmids occur in both gram-positive and gram-negative bacteria. and several different types of plasmids can exist in one cell: 1- Transmissible plasmids can be transferred from cell to cell by conjugation. 2- Non transmissible plasmids are small, since they do not contain the transfer genes.  Inclusion bodies (granules): Are nuclear or cytoplasmic aggregates of proteins. These granules function as: Food and energy storage e.g. glycogen, starch and metachromatic granules are a characteristic feature of Corynebacterium diphtheriae, the cause of - diphtheria  SURFACE APPENDAGES Flagella: a S The long filament, which acts as a propeller, is - composed of many subunits of a single protein, flagellin. They are responsible for motility. - Typical arrangements of bacterial flagella some bacteria have one, and others have many. In some, the flagella are located at one end, and in others, they are all over the outer surface. Only certain bacteria have flagella. Many rods do, but most cocci do not and are therefore non motile. rod have may not not have - most coce motive  & - & - ⑤ - O - & - E. coli pseudomanas  PILI (FIMBRIAE) Is a hair-like structures of protein subunits called pilin arranged uniformly along the whole surface of the bacterium Using these structures, for attachment to host cell receptors Pili have two important roles: Loading… (1) Short, they mediate the attachment of bacteria to specific receptors on the human cell surface, which is a necessary step in the initiation of infection for some organisms. (2) Long, a specialized kind of pilus, the sex pilus, forms the attachment between the male (donor) and the female (recipient) bacteria during conjugation and thus for transfer of plasmids  CAPSULES AND LOOSE SLIME The capsule is a gelatinous layer covering the entire bacterium. It is composed of - polysaccharide, except in the anthrax bacillus, which has - a capsule of polymerized D-glutamic acid. E s & It is considered as a virulence factor & Antiphagocytic & and as an adherence factor. Not all bacterial species can produce capsules, Encapsulated species are found among both Gram- # & positive and Gram-negative bacteria. Capsular polysaccharides are used as the antigens in certain vaccines.  LOOSE SLIME (GLYCOCALYX) Polysaccharide coat similar to capsule but secreted extracellularly, thinner and less rigid than capsule. Allows the bacteria to adhere firmly to various ⑧ 220 structures (e.g., skin, heart valves, prosthetic joints, God catheters and surface of the teeth). The finding that it is the glycocalyx-producing strains of: 1. Staphylococcus epidermidis and viridans streptococci that cause endocarditis. 2. The glycocalyx also mediates adherence of Streptococcus mutans, to the surface of teeth. This plays an important role in the formation of plaque, the precursor of dental caries.  SPORES o Some gram-positive bacteria but NEVER gram-negative ones produce spores -G under harsh conditions. o Endospore “spores”: is a highly resistant phase, the organism can survive in a ~ & & sig dormant state through a long period of dehydration, starvation and under harsh & environmental conditions even if there aren’t any nutrition. What are the stimuli for sporulation? Starvation (when nutrients, such as sources of carbon and nitrogen, are depleted). These highly resistant structures are formed by two genera of medically important gram-positive - rods:- the genus Bacillus, - which includes the - agent of anthrax, and the genus Clostridium, which includes the agents of tetanus and botulism. -  SPORES What are the layers of an endospore? & & 1- The central core: contains a single strand of DNA and high content of Calicium dipicolinate. 2- The cortex layer: which contains a double layer of peptidoglycan, which is more - resistant. 3- The spore coat: contains special hard resistant protein. 4- The keratinized exosporium: contains keratinized resistible Spores resistance due to many factors as: > - - > impermeability of their cortex and outer coat. their high content of calcium and dipicolinic acid. low content of water. All these factors enable spores to remain viable for many years in the dry state.  SPORES Spores stained by specific methods, appearance of mature spores vary according to species being: spherical ovoid or elongated, occupying a terminal, sub terminal or central position and being narrower than the cell or broader and bulging it. ↑ jo They are highly heat resistant and are not killed by many disinfectants. Germination: is the reactivation of spores and occurs under stimulation of external condition that favors growth. Water and nutrients: they are required for germination which leads to a bacterium identical to the original one.  REFERENCE S 1. Reidle, S., Morse, S. A., Meitzner, T., and Miller, S. 2019. Jawetz, Melnick & Adelberg’s Medical Microbiology , Twenty-Eight Edition. The McGraw-Hill education, Inc. USA. 2. Review of Medical Microbiology & Immunology: A Guide to Clinical Infectious Diseases, 16th edition 2020